HANDLING OF SEGREGATING GENERATIONS

PBG-301 FUNDAMENTALS
OF PLANT BREEDING AND
GENETICS (2+1)

HANDLING SEGREGATING
GENERATIONS
B.SUBHASH
2018042069

SEGREGATION
This term has two meanings in genetics and plant breeding:
• Segregation can refer to the separation of genes and their respective alleles
during meiosis into new daughter cells.
• This is also referred to as Mendel’s first law or the Principle of Segregation.
• can also refer to a population in which there is phenotypic variation.
• For example, a population may have both resistant and susceptible individuals
with respect to bacterial spot.

SEGREGATING POPULATIONS
 Populations like F2, F3 etc are called segregating populations.
 Techniques of selection like mass selection and pure line selection cannot be
applied to such populations.
 The methods of selection generally used in the case of segregating
populations are pedigree method, bulk method and single seed descent
method.

Handling Segregating generations
1. Pedigree method
2. Mass pedigree method,
3. Bulk method
4. Single seed descent method

PEDIGREE METHOD
 This method was first described by H.H.LOWE in 1927.
 PEDIGREE: ‘A description of the ancestor of an individual and it generally
goes back to some distant ancestor in the past’
 Thus, a pedigree would describe the parents, grand parents, great grand
parents and so on.
 The pedigree is helpful in finding out if two individuals are related by
descent their ancestry, and therefore, are likely to have genes in common.

PEDIGREE RECORD
 In pedigree method a detailed record of the relationships between the
selected plants and their progenies are maintained.
 As a result, each progeny in every generation can be tracked back to the F2
plants from which it is originated such as a record is known as PEDIGREE
RECORD.

PROCEDURE
 In pedigree method, individual plant are selected from F2 and the subsequent generations,
and their progenies are tested.
 During the entire operation a pedigree record is kept.
 Individual plant selection is continued till the progenies show no segregation. At this stage,
selection is done among the progenies because there would be no genetic variation within
the progenies.

ADVANTAGES
1. Provides the information about the mode of inheritance of various
qualitative characters.
2. Chance of recovering transgressive segregants by pedigree method.
3. Takes 14 to 15 years to release a new variety.
4. A high degree of genetic purity is produced in the cultivar.
5. The breeding value of selected plants is ascertained by progeny test.
6. Pedigree selection is based on genotypic value rather than phenotypic
value.

DISADVANTAGES
1. Handlingoflargeselectedmaterialisdifficult
2. Recordkeepingis slow, tedious,time- consuming,and expensive.
3. Since large number of progenies are rejected in this method,there
are chancesofelimination of somevaluablematerial.

Mass pedigree method
• It is a modification of pedigree method.
• Proposed by Harrington in 1937.
• Refers to growing of segregating material by bulk(mass) method when conditions
are unfavourable to selection and
• use of progeny testing (pedigree method) when conditions are favourable to
selection.
• The bulk period vary from one to few generations depending upon the ocuurence
of favourable condition.
• The bulk period is terminated as soon as favourable conditions for selection
occur.
• For example: In Wheat dry season is not suitable for selection of straw strength
plant height, earliness and shattering.
• Hence breeder has to wait for normal season for effective selection.

 Bulk population method of breeding in self –pollinated crop is also known as mass
method or population method of breeding.
 It was first used by Nilsson Ehle in 1908.
 It refers to a species is grown in bulk plot (from F1 to F5 ) with or without selection, a
part of the bulk seed is used to grow the next generation and individual plant
selection is practiced in F6 or later generation.
 In this method duration of bulking may vary from 6-7 to 30 generation.

1) Hybridization: Parents are selected according to the objective of the breeding programme and crossed.
2) F1 Generation: The F1 generation ( 10 to 25 F1) is space planted and harvested in bulk.
3)F2-F6 – Generation:F2 to F6 generations are planted at commercial seed rate and spacing. These generations
are harvested in bulk. During these generations the population size should be as possible, preferably 30 to 50
thousand plants should be grown in each generation.
4)F7 Generation: About 30 – 50 thousand plants are space planted and out of this only 1000 to 5000 plants with
superior phenotypes are selected and their seeds harvested separately. Selection is made on the basis of
phenotypes of plants, grain characteristics etc.
5)F8 Generation: Individual plant progenies are grown in single or multi row plots. Weak and inferior progenies are
rejected and only 100- 300 individual plant progenies with desirable characters are selected.
6)F9 Generation: Preliminary yield trial is conducted along with standard variety as check. The evaluation of
progeny is done for important desirable characteristics. Quality test may be conducted to reject the undesirable
progenies.

3)F10- F12 Generation: Replicated yield trails are conducted at several locations
using standard commercial varieties as check. The lines are evaluated for important
agronomic characteristics. If lines are superior to the standard check, released as
new varieties.
4)F13 Generation: Seed multiplication of the newly released variety for distribution to the
farmers.

 This method simple, convenient and inexpensive.
 Little work and attention is required in F2 and subsequent generation.
 No pedigree record is to be kept.
 It eliminates undesirable types and increases the frequency of desirable types by
artificial selection.
 It is suitable for studies on the survival of genes and genotypes in
populations.
 There are greater chances of isolation of Transgressive segregates than
pedigree method.

 It takes much longer to develop a new variety.
 It provides little opportunity for the breeder to exercise his skill in
selection.
 A large number of progenies have to be selected at the end
bulking period.
 Information of inheritance of characters cannot be
obtained like that of pedigree method.

 This method has used in Barley crop for developing some
varieties from the crosses ( Allas X Vaughn), like Arival,
Beecher, Glacier, etc.
 In India only one variety “Narendra Rai” has been
developed in Brown Mustard.
 This method has a limited application in practical plant
breeding.

Pedigree Method Bulk Method
1 Most widely used Breeding method Used only to a limited extent
2 Individual plants are selected in F2 &
subsequent generations and individual plant
progenies are grown
F2 and subsequent generations are grown in bulk
3 Artificial selection ; artificial disease epidemics
etc. are an integral part of the method
Mainly natural selection. In certain cases artificial
selection may be essential
4 Pedigree Records have to be maintained
which is often time consuming &laborious
No pedigree records are maintained
5 Generally its taken 12-13 years to
release new variety
Takes more than 15 years.
6 Requires close attention of breeder from
F2 onwards
It is quite simple and does not require much
attention

 Single seed descent method is the modification of bulk method of breeding.
 But the modification is in such a way that it allows the equal survival of a segregates.
 The idea of this method was first suggested by Goulden (1941) and subsequently modified by
Brim (1960).
General principles involved in this method is that,
 only one ( single) seed collected from each of the F2 plants ( 10000 to 20000) and then bulked
to grow the next ( F3) generation.
 Similar practised is continued till F5 or F6 generation, when the plant would become nearly
homozygous.
 In F5 and F6 generation, when individual’s plants are selected and harvested separately.
 Their progenies are also grown separately in next generation. Selection is done among the
programme ad promising one is select to conduct replicated yield trails and quality test
conducted in F7- F8 generation and coordinated yield trial in F9- F10 generation.

 Single seed descent method advantages the generations with possible
speed in a conventional breeding method.
 It requires very little space, effects and labours.
 It makes the best use of green house and offseason nursery, facilitates
because in that two to three generations can be raised in each year.
 It ensures that the plants retained at the end population are random sample
from F2 population.

Disadvantages
 The frequency of getting desirable genotypes in the advanced
generation is reduced.
 The identity of superior F2 plants cannot be maintained , their
identity is lost.
 This method is applicable only to self pollinated crops.

HANDLING OF SEGREGATING GENERATIONS

HANDLING OF SEGREGATING GENERATIONS

More Related Content

What's hot

Similar to HANDLING OF SEGREGATING GENERATIONS

More from subhashB10

Recently uploaded

In this document

HANDLING OF SEGREGATING GENERATIONS